Firefox 4.0 has a combined Reload and Stop and Go button that appears at the right end of the location bar. To restore the Firefox 3 appearance you can use these steps:

Open the Customize window via "View > Toolbars > Customize" or via "Firefox > Options > Toolbar Layout"

• Move the Reload and Stop buttons to their previous position at the left side of the location bar.
• Set the order to "Reload - Stop" to get a combined "Reload/Stop" button.
• Set the order to "Stop - Reload" or separate them otherwise to get two distinct buttons.

You can do the same with the Home button

Just want to add something onto cor-el answer. If you don't see the "Reload" button in the "Customize" window, you'd have to drag the "Reload" button from the location bar into the window, from there, you can drag it to anywhere you like. I found this out because I didn't see the "Reload" button in the "Customize" window and thought I couldn't do anything about it.